Such a probe device is known from European Patent Publication No. A1-54537 and its equivalent, U.S. Pat. No. 4,404,284. The device described in that publication is intended for the measurement of volatile components. It has a probe body which consists of three essentially tubular parts which are inserted into one another. A finger-like pin is provided at the front end of this device, which pin carries a permeation membrane and has a permeation canal formed by flutes on its outside. A sensor is connected to instrument leads inside the probe body and the carrier medium, which carries the permeated components with it, is fed via an axial blind hole provided in the said pin. The complex structure of this prior art device, consisting of a relatively great number of individual parts, is disadvantageous means, and manufacturing the various individual parts with correct fit and connecting them to each other are also difficult. For example, a turning operation as well as cutting a thread with extraordinarily exact fit is necessary for attaching the pin carrying the permeation membrane to the actual probe body. Due to the various parts which have to be connected to one another, the prior-art design also has sealing problems. There are also difficulties due to the fact that because of their numbers, the tubular parts need to have the smallest possible wall thickness to prevent the overall diameter of the probe means from becoming too large. Consequently, specially designed mounting flanges, which are provided with an O-ring seal in their inner walls, are needed for the fastening of the probe means in a wall opening of a fermenter, i.e., it is not possible in the prior art probe means to use conventional standard connection pieces which have no seals.
Another disadvantage of the prior-art probe is that the permeation membrane may easily be damaged during insertion, e.g., if the mounting flange or connection piece is lightly touched by the pin carrying the permeation membrane during the insertion. Finally, it is also difficult, if not impossible, to change the exchange surface on the pin for adjustment to various concentrations of the components to be measured, and it is also problematic to provide corresponding long or deep axial blind holes in the pin--which normally consists of a precious metal--if large exchange surfaces and hence long pins are needed.
The multicomponent design of the prior-art probe was considered to be necessary for the sensor to be able to be accommodated directly inside the probe body thereby keeping the carrier-medium canal between the permeation canal and the sensor short. If, however, no sensor is to be disposed inside a probe, a simple cylindrical pin or bar can be used, which has the helical flutes serving as a permeation canal on its outside, which said flutes are connected with paraxial bores serving as carrier-medium feed and return lines, and the tubular permeation membrane is pulled over the said bar or pin, see, e.g., German Offenlegungsschrift No. 2,310,264. However, similar to the devices known from French Patent Publication No. 1,573,147, this prior-art probe has the disadvantage that the carrier medium containing the permeated substances has to be fed to the sensor located in an external measuring and analytical instrument via a capillary tube, which is disadvantageous, because, e.g., of fluctuations in temperature, as is explained in European Patent Publication No. A1-54537.